text:
Why do gases in the combustion chamber only flow one direction to the gas turbine in a jet engine?
As far as I know from the working principle of jets engines, compressed air in the combustion chamber (or combustion canister) is mixed with fuel. The ignited mixture expands backwards to turn the turbine rotors and perpetuates the work cycle. Eventually, the left over hot gas creates the thrust.
Although heated gas expands in every direction in space, why does the combustion-gas only expand in one direction, towards the turbine?

I asked that on Physics once. I'm not convinced I managed to explain to any of the responders what my question was.

Note that there are two ways to look at this: steady-state and engine start. If the engine wasn't running in the first place, you probably wouldn't be able to start it by injecting fuel and igniting that. You need an external mechanism to spool up the engine and start the gas flow before you start the combustion. Combustion can sustain, but not start the gas flow. Note that in flight, you can restart an engine using the forward speed of the plane to provide that gas flow.

If you assume combustion chamber is the highest pressure point in the engine then of course gas would want to flow both ways. But that's not true. The combustion chamber is the highest temperature but the compressors exit has the highest pressure, so the gas only flows towards to turbine side.

@albin that video is not available any more :/

@HughPerkins  you can find the working link at here https://youtu.be/gUA4xfmgSGI

Thanks! I actually created a new video in the meantime at https://www.youtube.com/watch?v=dCX8CHAlpFc

It is actually not that simple to ensure the proper gas speed in a gas turbine. In the compressor you want to limit the flow speed over the compressor vanes to the high subsonic range, so the inlet has to decelerate the flow down to approx. Mach 0.4 - 0.5. Less would mean less throughput and consequently less thrust.
This speed, however, is far too high for ignition. The fuel needs some time to mix with the compressed air, and if flow speed is high, your combustion chamber becomes very long and the engine becomes heavier than necessary. Therefore, the cross section leading from the compressor to the combustion chamber is carefully widened to slow down the airflow without separation (see the section below named "diffusor"). Around the fuel injectors you will find the lowest gas speed in the whole engine. Now the combustion heats the gas up, and makes it expand. The highest pressure in the whole engine is right at the last compressor stage - from there on pressure only drops the farther you progress. This ensures that no backflow into the compressor is possible. However, when the compressor stalls (this is quite like a wing stalling - the compressor vanes are little wings and have the same limitations), it cannot maintain the high pressure and you get reverse flow. This is called a surge.
The graph below shows typical values of flow speed, temperature and pressure in a jet engine. Getting these right is the task of the engine designer.

Plot of engine flow parameters over the length of a turbojet (picture taken from this publication)
The rear part of the engine must block the flow of the expanding gas less than the forward part to make sure it continues to flow in the right direction. By keeping the cross section of the combustor constant, the engine designer ensures that the expanding gas will accelerate, converting thermal energy to kinetic energy, without losing its pressure (the small pressure drop in the combustor is caused by friction and the Rayleigh effect). Now the accelerated flow hits the turbine, and the pressure of the gas drops in each of its stages, which again makes sure that no backflow occurs. The turbine has to take as much energy from the flow as needed to run the compressor and the attached pumps and generators without blocking the flow too much.
The remaining pressure is again converted to speed in the nozzle. Now the gas is still much hotter than ambient air, and even though the flow at the end of the nozzle is still subsonic in modern airliner engines, the actual flow speed is much higher than the flight speed. The speed difference between flight speed and the exit speed of the gas in the nozzle is what produces thrust.
Fighter engines usually have supersonic flow at the end of the nozzle, which requires careful shaping and adjustment of the nozzle contour. Read all about it here.

"The rear part of the engine must block the flow of the expanding gas less than" less? Moire maybe?

@rbp: No, less is right. The flow always takes the path of least resistance, and if the turbine would block it more than the compressor, you get a surge.

@PeterKämpf What is the model of this jet engine?

@albin: I don't know myself. I googled the picture and think it shows the basics nicely. For a regular engine it has too little pressure remaining after the last turbine stage. It does not dive a big fan or a propeller, so there should be some energy left behind the turbine. The trend of the parameters looks right, however.

@PeterKämpf I have read that the combustion chambers are designed by considering the flow as Rayleigh flow. And in Rayleigh flow for subsonic case the static and stagnation pressures decrease during heat addition. So how does the pressure remain constant if we neglect the frictional loss.

@AbhishekPallipparagopakumar: Good remark, there is indeed a drop from the Rayleigh effect.

The air in the compressor is both compressed and moving downstream towards the combustion section. The combustion does not create enough pressure to overcome all of that, and there is lower pressure as the air gets expanded through the turbine sections.
When the pressure in the compressor section drops too much, the combustion flames do expand in both directions. This is called a "compressor surge".

Disclaimer: I may have spent several hours on Wikipedia at one point trying to answer this question for myself!
Jet engines use the Brayton cycle, which is a "isobaric" process during combustion, meaning it keeps pressure constant during that phase.  This is in contrast to the Otto cycle of a typical four-stroke piston engine, which is "isochoric" during combustion, meaning it keeps volume constant during that phase.
The Brayton cycle consists of 3 parts, of which combustion occurs in the middle

Incoming air is compressed.  This requires work which is supplied by turbine at the end of the cycle while the engine is operating or an external motor when starting the engine.  This raises the pressure of the air (decreasing the volume).
Fuel is mixed with the air and ignited.  This is a continuous process (unlike piston engines).  This process is "constant pressure," which is the part that you are asking about.  It's not intuitively obvious why, so we'll dig into it in the next section.  The end result is a larger volume of air at the same pressure as the inlet to the chamber from the compressor.
The air is passed through a turbine in a shape which decreases the pressure from the compressed pressure to atmospheric pressure.  It uses this turbine to run the compressor.  All pressure differential which is not needed to power the compressor is used to accelerate the air backwards to provide thrust.

So how does this "constant pressure" thing work?  Treat the combustion chamber as a sort of box for a moment.  Whether there is combustion or not, there's going to be generally constant pressure inside the box.  Air is being pushed into it by the compressor, with some velocity and pressure.  If the turbine at the end of the chamber can "dispose" of air at a high enough velocity, it can keep the pressure at the far end of the chamber equal to that of the front end.
So how does this "constant pressure" thing actually keep the flame front from advancing forward?  The trick is that the flame front is trying to advance forward, but the velocity of the air through the chamber matches the speed of the flame front, keeping it in a constant location in the chamber.  This is a dynamic process, so we'll need some dynamics.  They key detail is that the turbine and compressor are on one axle, so what happens to one affects the other.
Consider three cases which compare the airflow velocity to the fuel:

Too slow for combustion rate — this happens if you increase the throttle, or at the starting of the engine.

The combustion starts to win, advancing the flame front towards the compressor, just like you'd think it would.
However, now the dynamics come in.  As the flame front moves forward, it raises the pressure at the outlet of the compressor, slowing the velocity of air through the compressor.
This means the compressor doesn't have to pressurize as large of a volume of air, so its load decreases.

(The compressor IS having to pressurize the volume to a higher pressure, but its trivial to see that this effect is overshadowed by the decreased volume of air by considering the edge case of a very weak compressor which clearly backs up if you pressurize it from the other side.)

The turbine is still seeing the same pressure, but its less loaded.  This spins the turbine up, increasing air flow leading us to...

Trimmed engine — This is where planes normally try to operate, and it's where you don't see flames propagating forward.

In this state, the velocity of the incoming air is enough to match the flame front's propagation forward.
The flame front keeps trying to move forward, but air is shoved in front of it just as fast as it can burn.

Too fast for combustion rate — this happens if you decrease the throttle.

With less fuel, the flame front begins to fall backwards towards the turbine.
As in the "too slow" case, dynamics come into play.  As the flame front moves backwards, this also decreases the pressure on the inlet to the combustion chamber, and the compressor.
The turbine now sees more load, spinning the turbine down.  Slowing the turbine decreases airflow through the compressor, bringing us back towards a trim engine.

One takeaway from this pattern is why jet engines cannot change thrust quickly.  If you rapidly add fuel by throttling up, you choke the engine, so you don't get much extra power until the turbine and compressor can spin up to equalize the engine.

A flame front is only possible in a fuel/air mixture. The engine has fuel injectors only at the start of the combustor, where the flow speed is 20 - 40 m/s - way below any flame front speed. Ahead of this no fuel is present if the pressures are right. Actually, the combustor needs small flame holders to make sure that the flame remains in place!

@peterkampf I think you wrote that backwards. 20-40 m/s is way higher than the flame speed of any practical fuel.

@XRF: You're right, and I did not know that four years ago. That makes flame holders essential.

I happened upon this question, and thought I could add some information, as I recognized the powerplant right away.
This is not another full answer, but only a response to @albin and @PeterKampf as to the engine model.  I cannot yet add comments, so edit this as is necessary.
The engine picture you used in your answer is the power section of the Allison 501 series, which had several civil and military aircraft applications. The reduction gearbox and propeller was omitted from that picture (for whatever reason).  That omission is confusing, please see my image below for the whole picture of what is happening in that powerplant.  Usually an Aeroproducts or Hamilton-Standard propeller was fitted.
@PeterKampf, you were on the right track - there is little energy left over for jet thrust after the turbine has extracted it because most of the power needs to drive the RGB and propeller.  Very typical of a turboprop (or turboshaft, for helicopters) design - residual jet thrust is of little use.  In this case, given certain atmospheric conditions and at on-speed RPM (13,820), the turbine can extract roughly 10,000 horsepower from the gas stream.  It takes ~6000 HP to drive the compressor, which leaves about 4000 shaft HP for the RGB and prop.
The Convair 580 uses 2 of these powerplants, The Lockheed C-130 Hercules uses 4.
If this were a turbojet design, the engine would likely have only 2 turbine stages instead of 4.  This would extract only enough energy to drive the compressor (and thus self-sustaining the engine), with plenty of thrust left over for use.

Welcome to aviation.SE. please be aware that this is not a discussion forum, but a Q&A site. I realize you want to comment on other answers, but this will only be available only after some positive contributions. Please stick around and you'll be able to comment under any post.

well, I for one found Bronco6363's response extremely useful. For example, I appreciated the details about how much power can be extracted from the turbine, how much is needed to drive the compressor (over half!), and so on.


text:
What impact did the Concorde have on business of other sub-sonic airliners?
The Concorde was anyways a technical marvel of its time, and a status symbol for society. Its fares were well above the rest, costing USD2999 + taxes for a JFK-LHR journey. But, at the same time there are reports that British Airways indeed made $750 million from it, over 27 years:

It was not that Concorde operations made losses. In fact, on an
  average Concorde made an operating profit of £30-50 million a year
  for BA. BA reportedly earned £1.75 Billion in revenue for Concorde
  services against an operating cost of around £1 billion during its 27
  years of commercial operation (1976-2003).

So, what impact did it have on the business of other sub-sonic airliners? Probably, economy class would not have been so much stricken, since its fares were more than 3 times higher. But what was the impact on business class travel of other airlines and airliners, between the destinations served by the Concorde?

I would guess that subsonic first class lost precisely as many travelers as there were tickets sold on the Concorde. Though, it might have been even less - those who chose to fly Concorde may have done so at the expense of private jets or charter, not public first class, either for the speed or the status.

With 14 planes made and 100 passengers, the impact would be very limited passenger wise.

A few thoughts:

The British Airways Concordes only operated scheduled on the London Heathrow- New York JFK route. This implies this is the route under the most competition. There has been enough pressure on this route even after the demise of the Concorde for several companies (as well as BA) to try business-only services on this route.
By experience, changing flights is never quick in the US since you need to go through customs and add time margin to ensure you make the connection (Think three hours connection time on the ground). I think even before the current security state you'd rather have taken a direct flight than change from a Concorde to a domestic flight if possible.
I don't think the charter destinations would have caused much impact on other airline operations.

As told, Concorde is one of the technical marvels of man. It wouldn't have large impact on economy but, it definitely had a huge impact on business class. Concorde would take less time than the subsonic flights, the person choosing business class would as well choose Concorde for the same destination because TIME is one of the major factor. Concorde travels much faster than subsonic.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
What damage can occur and what penalties will you face for flying a quad rotor into a restricted airspace?
I live near the Cleveland International Airport. I have a Quadrocopter and the fence doesn't seem to be very high. I could probably fly my quadcopter into the airport. Is this legal? Can I crash a plane with it? Is this a new terrorist attack vector? Will the airport security try to jam radio signals or something?
This is just a hypothetical question. I do not intend to wreak havoc and crash planes.

@fooot This might be useful to you: SE Comment Link Helper

While I was researching this issue more after my answer, I ran accross this forum thread:http://www.rcgroups.com/forums/showthread.php?s=7bc9d201d892b4b0092919c26e8cd40f&t=2014228 I will no longer participate in this question, as I have no desire to replicate these arguments. The laws are not totally decided, at least as far as r/c aircraft. The FAA has made some decisions that have been sucessfully fought here in the US, but in today's post-9/11 society, personnaly, I wouldn't push it, YMMV.

I'm surprised how much questions are about assessing responsibility in case of RC or quadcopter accident. The principle is that you pay to repair damage that are the consequences of your acts, even if you didn't do anything illegal (civil responsibility). This is the reason why the insurance business exists. In addition if you did something illegal, then you face a prosecution by the State and the penalty stated in the law (criminal responsibility). In addition if you did harm intentionally, then the penalty will be maximized.

The legal issues are covered in another question. The FAA doesn't currently regulate recreational model aircraft operations, which includes quadcopters.
Were you to actually fly it over the fence, you could be charged with trespassing. If you had any intent to cause harm, other charges might apply (up to attempted murder if you were trying to bring down an airliner).

Can I crash a plane with it?

Not likely. If you flew the quadcopter into a jet engine intake, you might be able to shut down the engine (similar to ingestion of a bird). This would really annoy the flight crew but would normally not result in a crash. A strike in any other place is probably going to merely dent something on the plane, and utterly destroy your quadcopter. For a small plane, shattering the windshield is a possibility, and this would be a serious hazard that could cause a crash, but is quite unlikely. Without some kind of advanced guidance system, it's going to be very hard to hand-fly the copter into a plane at all, let alone precisely target a vulnerable point.
The bottom line, though, is don't do it.

Is this a new terrorist attack vector?

Maybe! The use of unmanned aerial systems by terrorists is a subject of concern and research in the defense community. The RAND Institute has published a whole book about it.
Drones are already being used by drug cartels to smuggle drugs across borders. There have also been some high-profile incidents where terrorists were able to tamper with, and in at least one case eavesdrop on, a U.S. military drone by obtaining and decoding its live video feed. I don't know of any publicized instances of someone intentionally causing damage with a UAV or model airplane, but I'm sure the terrorists are thinking about it.

The drug cartel link doesn't actually say that cartels are using drones. Everything in there is "won't be impossible" or "eventually".

"This would really annoy the flight crew..."
Not to mention the insurance company that is now on the hook for a jet engine that costs at least a few million and up to about $30 million. Expect a pretty serious lawsuit, in addition to whatever criminal charges you may face.

There's an episode of "Person of Interest" where an assassination is carried out by an explosive-laden drone

@rbp if memory serves, it's an attempted assassination, and it's done by an ASI hacking its way into a Predator (military) drone.  Although on second though, I'm not sure about the ASI part.

First off, it is VERY important to note that you DON'T fly a Drone. RC Model Aircraft are flown by hobbiests, and Drones are flown by the government. It is enumbant on all of us R/C modelers to enforce that at all times, lest the government decide that all R/C hobbiest model aircraft be banned.
(I am making an assumption that you aren't doing this as a member of the armed forces, or working for the government, also my comments are US oriented.)

FAA Modernization and Reform Act of 2012
Senate Bill, Section 607(g) …exempts most model airplanes used for recreational or academic use from any UAS regulations established by the FAA
Conference Committee Report
Senate bill with modifications… Language including model aircraft for the purposes of sports, competitions and academic purposes is removed and replaced with "hobby". The modified section includes language requiring that the model aircraft must be operated in a manner that does not interfere with and gives way, to all manned aircraft. In addition, language that requires that model aircraft flown within five miles of an airport will give prior notification to the airport and the air traffic control (ATC), and that model aircraft that are flown consistently within five miles of the ATC will do so under standing agreements with the airports and ATC. Lastly, language is added that will ensure that nothing in this provision will interfere with the Administrator's authority to pursue enforcement action against persons operating model aircraft who endanger the safety of the national airspace system. In this section the term "nationwide community-based organization" is intended to mean a membership based association that represents the aeromodeling community within the United States; provides its members a comprehensive set of safety guidelines that underscores safe aeromodeling operations within the National Airspace System and the protection and safety of the general public on the ground; develops and maintains mutually supportive programming with educational institutions, government entities and other aviation associations; and acts as a liaison with government agencies as an advocate for its members.

SEC. 336. SPECIAL RULE FOR MODEL AIRCRAFT.
(a) In General. --Notwithstanding any other provision of law relating to the incorporation of unmanned aircraft systems into Federal Aviation Administration plans and policies, including this subtitle, the Administrator of the Federal Aviation Administration may not promulgate any rule or regulation regarding a model aircraft, or an aircraft being developed as a model aircraft, if--
(1) the aircraft is flown strictly for hobby or recreational use;
(2) the aircraft is operated in accordance with a community-based set of safety guidelines and within the programming of a nationwide community-based organization;
(3) the aircraft is limited to not more than 55 pounds unless otherwise certified through a design, construction, inspection, flight test, and operational safety program administered by a community-based organization;
(4) the aircraft is operated in a manner that does not interfere with and gives way to any manned aircraft; and
(5) when flown within 5 miles of an airport, the operator of the aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation (model aircraft operators flying from a permanent location within 5 miles of an airport should establish a mutually-agreed upon operating procedure with the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport)).
(b) Statutory Construction. --Nothing in this section shall be construed to limit the authority of the Administrator to pursue enforcement action against persons operating model aircraft who endanger the safety of the national airspace system.
(c) Model Aircraft Defined. --In this section, the term "model aircraft" means an unmanned aircraft that is--
(1) capable of sustained flight in the atmosphere;
(2) flown within visual line of sight of the person operating the aircraft; and
(3) flown for hobby or recreational purposes.

When this law is passed, you'll need to contact the airport tower/operator if you intend on flying your model aircraft within 5 miles of the airport.
If, at the time of this answer, the law has not yet passed, the rules prior were to keep your model aircraft under 400ft AGL within 3 miles of an airport. Flying your model aircraft over the boundary fence OF an airport is considered tresspassing and an incursion.

I found specific laws for the UK as well, but this answer wore me out, so I'll stop here.

Also, it'd be interesting to do a map of an area (like I live in Northern Virginia, USA) and flag all airports with a 5 mile radius, just to see how much airspace is left. :)

If you count private farm strips as "airports," probably not very much indeed, at least in that part of the country and mine (the Midwest prairie)!

The 400 ft./3 mile bit isn't actually a law is it?

It is not. It was a general rule to follow, but not an enforceable law with penalties attached. However, as short as just a few years ago, flying model aircraft was kind of a specialist hobby. We went to Toys'R'Us last night, and there is a quad-copter for sale for under $200, fully capable of carrying a small camera and with a fully featured control set. Everyone decries Amazon for thier "drone delivery", yet last night four neighbors were dogfighting their quads out back...

I should add that the law I quote above, in other sections details other than hobby r/c aircraft. If you fly a r/c aircraft or quad, for commercial purposes, you're going to want to carefully read the new laws. R/C Model Aircraft hobbiests are exempt (still) from many of the laws/requirements. Any government entities (local/state/federal) and commercial organizations desiring to utilize unmanned r/c aircraft are going to be facing much, much, MUCH, tighter regulations.

According to http://beta.congress.gov/bill/112th-congress/house-bill/658, HR658 became "Public Law No: 112-95" on 2012/02/14 (after being passed by both the House and the Senate in April 2011).

Thanks for that. What I read looked like it was current and that it was a 2013 bill.

I'm by no means an expert and am probably incorrect, but my perception of a "drone" vs an "RC" is that a drone is capable of sustained flight without human involvement. Where-as an RC aircraft must have human interaction to maintain flight. For example, military drones can be given coordinates or flight paths and they will fly / navigate autonomously. A UAV, on the other hand would be both of those.

@Tom Not true. There is no technical difference and there is no official definition either AFAIK. RC's with auto-pilot exist. Standard convention seems to be that Drone is military. Everything else is considered RC.

[soapbox] Since this isn't about the laws/regulations, I'll comment. What I meant by the first lines above was that we hobbiests who use R/C Model Aircraft, IMHO, should never EVER use the word Drone to describe that thing we are flying. EVER. I don't care whether it is a VLOS, camera controlled, auto-piloted, GPS, or whatever. If we start calling them drones, then when the goverment decides to regulate against 'drones' for protection from fear of ...whatever, assasination, big brother, privacy... then our hobby will simply, in one fell swoop be made illegal. I don't drone, I model. :)

We MUST self-regulate, consistantly, thouroughly and constantly. If we, as a group, continue to state "we do NOT fly drones, we never fly drone, we fly Radio Controlled Model Aircraft, then we are more likely to be able to distance ourselves from anti-drone legislation. My 2 pisetas. [/soapbox]

Intruding in an airport's controlled airspace (typically class B or C airspace) or endangering an airplane is illegal. (This includes non physical interference.) Doing this as a pilot in a plane can get your license suspended by the FAA and NTSB.
When the tower sees unauthorized entry of a drone they will clear the airspace and send security to catch the guy controlling it.

What if the quad has cameras on it and is being controlled from long range. How are they going to take it down? Shoot it?

Well, there have been incidents of LASER pointers illuminating aircraft and the users tracked down whereupon they were charged with a crime. ( http://www.laserpointersafety.com/news/news/aviation-incidents_files/tag-customs.php ) My assumption would be they would find you and clip your toenails with a soldering iron. :)

Umm, what makes you say that flying into an airports airspace is illegal?

@Lnafziger major airports are class B or C airspace which require ATC clearance.

@ratchetfreak Yes, for pilots. I'm pretty sure that there isn't a law that covers RC airplanes though, even if it would be incredibly stupid to do it. See the question linked in dvnrrs's answer.

@Lnafziger but you can be charged with trespassing and endangering, and the damages of the interference of the airport's operation

@Lnafziger actually YOU are the pilot of your air vehicle. US law doesn't differentiate for RC airplanes so they are included by default in the laws that do exist.  Particularly in this antiterrorist climate, you would be very stupid to fly even a toy that close to an airport, you will not get the benefit of the doubt.

@JamesRyan Last I checked, a pilot license wasn't required in order to fly one.  :)  See the first link in dvnrrs's answer for more specifics on the actual laws. I agree with your last sentence though, and said almost the same thing three comments ago.

@Lnafziger True, but a drivers license is also not required to operate a bicycle, meanwhile you still can theoretically get charged with a DUI in many states for riding a bike drunk! In many jurisdictions, the bikes are still considered "vehicles" and must theoretically obey the same laws of traffic, as crazy as that is...

@Ruslan, As mentioned in CGCampbell's post, there actually IS a codified legal distinction between RC model aircraft hobbyists and actual aircraft pilots. FAA regs explicitly do not apply to RC hobbyists.

If the aircraft model can listen to your transmitter, so can the search teams. en.wikipedia.org/wiki/Transmitter_hunting

In the UK the definition of aircraft is very small and light only a few kg - not big enough to carry a person thats for sure.

The big problem with flying even small models near aircraft, is this: the model might only weigh a few kg and not fly very fast. Lets say 5kg and 40mph.
So you fly it near a light aircraft thats coming into land. This is doing 70 knots = almost 80mph. Thats a 5kg hard (ish) object hitting something at 120mph. If it hits the pilots windscreen, which is only thin perspex, it could kill or badly injure the pilot and everybody on board could be killed.
If you apply this to a jetliner, sure it might be harder to smash the windsceen, but the jetliner is doing 130 knots on approach - going on 150mph, so that makes a 190mph closing speed, which again could do a lot of damage. Even if the model is hovering, the closing speed is still the speed of the large aircraft and the amount of energy in the impact is related to the square of the speed and the weight, so double the speed at a given weight, you get four times the impact.
There should be no question in my mind, by all means play with these things, but if you have a loaded gun, most sane people would keep well away from pointing it at somebody. If you have any thought for other people (and your own conscience and freedom), then it should be the same with these things.

The speeds of the objects do not add up. The plane will hit an object while going 80. Some damage will occur. The to objects as determined by their mass will continue moving unless acted on by another Force.

What doesn't add up? If you have one object doing 40 and the other 80 and they hit each other head on thats a 120 closing speed. In the case of the jet, the drone doing 40 and the jet doing 150 is 190 assuming its head on. The point I was making was that you think your slow little drone isn't going to carry much energy, but the speed of the big aircraft adds to it, so a 5kg brick hitting something at 190 is a pretty hard hit.

Collision between airborne stone and car http://physics.stackexchange.com/q/242800 This was also discussed on MythBusters on more than one occasion. This "Wired" article shows one of them https://www.wired.com/2016/01/5-of-the-greatest-physics-demos-from-the-mythbusters/ I'm sure you would love for what you're saying to be true but it's not. After the impact the plane will be going slightly slower unless throttle is applied.

The article you refer to mentions possible effects on the subsequent trajectory. I'm approaching from a different angle. All I'm saying is that its not a 5kg object doing 40mph, the speed of the aircraft has to be taken into account when working out the momentum (the force that it hits with). Yes the initial trajectory of the heavy object won't be much different but depending on the subsequent damage, if the pilot is unconcious or the fuel cap of an airliner or engine has been damaged, what happens next could well be different.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What's the mechanical 'whoosh, whoosh' sound in this video?
Sound in question comes right after the warning sound at 22:57.

I'm voting to close this question as off-topic because Or associated with an entertainment simulator feature then a real airplane or aviation

That's a real sound. I just couldn't find a video with an actual cockpit footage.

It's the sound of the trim wheel rotating on the center console of the Boeing 737.
The trim wheel controls elevator trim. It can either be moved automatically by the autopilot, or manually by the pilot. The pilot can push the trim button on the yoke with their thumb (left for the captain, right for the copilot).

This is a photo of a B737 classic series, but this feature is unchanged on the NG series.
In this specific instance, it sounds like there were two small manual push on the trim button.

Thanks a lot for the response. I learned something new today thanks to you.

That is supposed to be the trim wheels? Somebody needs to work on the sound effects on that sim.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the tail strike pitch angle of the ATR-72?
What is the maximum pitch attitude an ATR-72 can be during takeoff or landing, without having a tail strike?

The FCOM says "tail strike may occur if pitch attitude exceed 8° during the flare
depending upon vertical speed at touch down" (Ctrl + F "tail", matches 31 and 32).

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How many hours to remove and install a Cherokee 180 engine and prop
How many hours should it take a shop to remove, install, and adjust the engine in a Cherokee 180 with a fixed pitch prop?
This would include the baffles and any hardware needed to be removed and installed for an engine swap.

I once changed an engine in the bush when I was bush flying, helping the air service's mechanic.  It was a C-180 on floats (I had been forced down in it after the engine developed a loose cylinder from failed hold-down studs).
There was a rigid dock for us to work with at the remote lake we were at, and we used a bipod made of pine poles with a come-along to lift the engine and set it down on the dock (with the noses of the floats against the dock).
It took about 6-7 hours to have the engine and prop removed and ready to be loaded on the company Beaver when it showed up around 5 pm (loading it was the really entertaining part).
We went back in two weeks later with an overhauled engine and installed it, 2 mechanics and myself, and I flew it out that late afternoon around dinnertime.
So for a Cherokee sitting in a hangar with a lift handy, one mechanic with an assistant, about 4-6 hours to remove the engine, and about 6-8 hours to install it.  Certainly no more than two days at most.

That's like a 2-4 day effort or more, depending on how many hands are helping, and what the condition of the removed items are. I saw a Cessna 172 get its engine replaced after an overhaul, these are all the things I remember being touched, and it was more than 4 days due to waiting for some parts to come in.

cowling
cowling mounts at front of engine
spinner, prop
baffles & springs, as you mentioned
attachments & accessories, including:
muffler & heat shroud
starter & wiring
magnetos (dual unit or 2 single units).  Does it/they need 500 hour IRAN?
alternator, belt, wiring
air hoses, maybe replace with orange SCAT hoses
carburator
throttle control
mixture control
carb heat control
all the engine probes, incluuding:
oil temperature
oil pressure
cylinder head temperature (may be 4)
exhaust gas temperature (may be 4)
fuel pressure
maybe fuel flow
maybe carb throat temperature
replace the engine mounts if they are old/stiff
fuel connection
oil filler/dipstick tube
oil filter (any adapters for spin-on filters)
oil filter screen
crankcase breather tube
vacuum pump
connections to oil cooler (and flush it out)

A lot of things are safetywired too, so that has to be all addressed as they go back on. Then securing all the wiring & hoses & tubing. My AP/IA won't let things be tiewrapped to the engine mount, ADEL clamps protect the engine mount and provide attachment points.
And I'm probably missing some things too. Then there's documenting it all.

Thanks so much for your details-Al


text:
What market share does Jet A-1 have in the commercial airline market?
I know that Jet A-1 is the most widely used fuel in the commercial airline market, but what is its market share in percentage?
Are there any big users of Jet A rather than Jet A-1? And if so, why?

Chevron writes

Jet A is used in the United States while most of the rest of the world uses Jet A-1. The important difference between the two fuels is that Jet A-1 has a lower maximum freezing point than Jet A (Jet A: –40°C, Jet A-1: –47°C). The lower freezing point makes Jet A-1 more suitable for long international flights, especially on polar routes during the winter.
However, the lower freezing point comes at a price. Other variables being constant, a refinery can produce a few percent more Jet A than Jet A-1 because the higher freezing point allows the incorporation of more higher boiling
components, which in turn, permits the use of a broader distillation cut. The choice of Jet A for use in the United States is driven by concerns about fuel price and availability. Many years of experience have shown that Jet A is suitable for use in the United States.

Notably, the US is also the single largest market for aviation fuel worldwide, so it has the volume to support a separate type. There's consumption numbers in the same document.
The disadvantage with Jet A is with long-haul flights that experience cold air, the 7 degrees can make a difference, forcing the flight to descend to warmer levels to heat the fuel, increasing consumption.
One thing that can be done is a sample of the loaded fuel is taken and the actual freeze point determined, and that number used in flight. Usually for Jet-A this lies somewhere in between the two specs.

I can't speak much for private jets but most airlines including Southwest, Delta, American, Allegiant, United, Onejet, Alaskan, Virgin, Aeromexico, and Fedex use jet A fuel.
Fedex uses planes such as the Cessna 208B Grand Caravan, the ATR 42 and 72. All three of these planes operate on Jet A with an FSII (Fuel System Icing Inhibitor) called Prist.
I work at IND and we don't supply any Jet A-1

I am pretty sure all of them take Jet A or Jet A-1 (they are different, but engines generally take either) depending on which is available.

I feel that, if you're going to directly contradict the claim made in the question, you ought to supply some evidence. You've listed ten airlines but all we have is your word that they use Jet A rather than some other fuel. (Honestly, some kind of citation would be good even if you're not contradicting the question, but it seems even more important in cases such as this one.)


text:
Can I log Hours in a foreign aircraft?
I have my FAA Private Pilot License but I live in Chile, The thing is that I was asked by the father of a friend of mine to join him on a C182 flight in Chile (Chilean Aircraft). So, can I log  that time in my Log Book? Even though I did my training in a C172 and don’t have the High Performance endorsement?

If it is a Chilean-registered aircraft you will most likely need to hold a Chilean licence to fly there.

The rule of 3 apply I think, if it was an american registred aircraft in Chile you can, if it was a chilean registred aircraft in US you can. But you don't seem to have 2 out of 3. So it will be a no I think.

Aside from the foreign location, it's a single pilot airplane and as such, you're going along for a ride and shouldn't be logging time, unless the owner is a flight instructor and you can log time as P2, or unless the owner is designating you PIC, in which case you'd better be on his insurance.


text:
What is the stick at the bottom of the tail on a ATR-72?
During my last flight I observed the ATR-72 has a stick protruding from the bottom of the fuselage, near the back of the airplane.
See the bottom of the fuselage in this picture, slightly to the left of the rear door.
I assume it impedes take off and must be removed before flight.
What is it?

Seriously, closed as duplicate?! A single answers mentions what it is, but it doesn't elaborate on it, nor is the question even remotely related (which aircraft has it, as opposed to what is it). You've effectively cut off the opportunity to explore the question deeper, and perhaps provide more elaborate - better - answers.

@mins The "older question" doesn't ask what it is. It appears the asker already knows that, wouldn't you agree? I mean come on, it's a completely different question. Why would you elaborate on the particulars of the ATR in a question (that frankly it would be more appropriate to close as too broad than to close this one as duplicate) that ask "which aircraft has a tripod". Note that the ATR doesn't have one, it's just mentioned as a reference for a different kind of support.

It is a tail stand, also called as pogo stick and is used in the aircraft during loading/unloading. It is basically a stick, which is carried around in the aircraft and attached to the rear fuselage using a pin during loading/unloading operations, as can be seen in the image below.

Air Dolomiti ATR 72-212A (I-ADLS) - Removeable tail stand installed at the rear of the aircraft when it is parked on the ground. In case of weight imbalance, this prevents the aircraft from resting on its tail. By User:Mattes - Own work, Public Domain, Link
It is found in other aircraft like Saab-Scania SF340B etc.
You're right that it must be removed before takeoff to prevent potential structural damage. However, there have been instances where aircraft have taken off with them. There have been other issues too:

First of all, there have been previous incidents where the ground crew have just tossed the tail stand into the aft compartment and not replaced it into the storage bracket. As a result, the tail stand has gotten jammed into the control cables for the tail surfaces which run through that compartment. ... . The second reason is that being less visible, the built in tail stand would occasionally be left connected to the aircraft on departure creating the potential for structural damage.

Because of this, external metal stools are used in some cases. Of course, the aircraft can be loaded/unloaded without the tail stand by loading the aircraft in appropriate sequence.

It appears to be a pogo stick  (you'll find your picture used in the linked answer) and is a precautionary support for the tail to prevent it from tipping over when loading and unloading.


text:
Can you become a pilot with an Asperger syndrome diagnosis in Europe?
I have the diagnosis results for Asperger syndrome (scored 177 out of 76 required to get the diagnosis). Are there any regulations in Europe that can stop me from achieving my life goal: To fly commercial jets?
My autism makes me very strongly interested in aviation, programming and audio design. But aviation is absolutely on top and has been since I was 6. The others have come as I age.

It might be a little off-track: So I'll add this little story just to add some "meat" to the question:
I just recently went on a trip with a few of my co-workers that included a trip on a B737-800. They thought it was special that I filmed the takeoff and landing, took pictures of it at the gate, and viewed out the window the entire two hours trip (my neck still hurts). They also had a funny reaction when I explained why the airflow to the cabin (packs) suddenly went silent as the engines start up. There is nothing more that I enjoy than flying, and I feel like I really belong up there (that poor kid in the seat in-front of me had a very different opinion).
I really wanted to see the cockpit during these flights. But asking is hard for me with Asperger. It kind of makes me feel like a 4-year-old.
It might not count for much in the real world, but I have logged over 16,000 landings on my little home-simulator. Three of them are intended crashes just to test the simulation.
All I ever wanted since I was a kid was flying commercial jets.

Related

"I think first you should figure out whether you like flying airplanes or not as a love of aviation and airplanes does not automatically mean you will love being at the controls."  -- Best advise. I wanted to be a pilot really badly, so my Grandfather took me to the airport and a friend showed me what it was like. I gave up on that goal right then an there. It was not what I imagined.

There's a big difference between flying privately and commercially as well. With private flying you go where you want and when, commercially it's a job and you have all the paperwork and politics to go with it. A captain of an airliner's not just a pilot, he's a manager of the crew and passengers on it. It's not always fun.

It sounds like you have a technical interest in aviation as well. You should investigate the maintenance positions in avionics or the mechanical side. Many pilots with low hours switch to that side as the pay is usually better in the early days. Plus the medical requirements are a lot less. Your maintenance licence will allow for ground run ups and test runs down the runway. Hope that helps.

Even if you would have asked, you would most certainly not have been allowed to visit the cockpit during flight.  This is just not done anymore.

@J... I meant to ask as I passed the flight attendants when boarding / disembarking :)

Aspergers is a fairly recent category.  Given the technical nature of flying -- aerodynamics, systems, regs, weather, etc -- I'm betting thousands of pilots with undiagnosed aspergers have been certified. I know many.

A commercial passengers pilot primary job is to control the passengers and decide what to do when there are issues with people.  Flying can mostly be done by computer when it all goes to plan.   So lots of people skills are needed including being good a dealing with people when you are stressed etc.

It does not seem a very debilitating disease, one that allows for great concentration and methodical skills. I reckon over 80% of students at a technical university have it :)

This is an old thread but I really, really hope that you did not let anyone here or elsewhere deter you from getting into a cockpit. The first stop is trying to get a medical certificate class 1. If you can get past this, the rest is just flight training. Be wary of the non-pilots who adopt advisory tones on the internet. The facts are: a license and medical certificate are what you need to exercise the privileges of the former. Landing a job with an airline is about passing a job interview. People without Asperger have tried and failed. I'm sure that others with it have succeeded.

In order to fly commercial you will need a first class medical certificate, and getting that with aspergers is going to be tough. The first consideration is the safety or people in the air and on the ground, so the criteria is conservative. Getting a first class medical would mean lots of extra hoops, even if it is possible. If you did get a medical you would then be competing against candidates who are neuro-typical, and would have to convince the airlines that you would be able to perform your job as well as non-aspergers candidates. That's not to say it's impossible, you would want to talk to a few aviation medical examiners about it to see what they say. If you can get a medical then you've got a chance, and if you are motivated enough and willing to work for it then I believe where there's a will there's a way.
You need to consider your own temperament when going for a pilots license of any kind, whether aspergers or neuro-typical. Flying is not just about the technical details, you need to be able to work with people, first of all your instructor! In commercial flying you also need to cooperate with other pilots and work with passengers, ground crew, and cabin staff. The extreme focus on detail and depth of knowledge on aviation you might develop with aspergers can be a huge asset in some ways, however aspergers could make it very challenging to work cooperatively in the cockpit, deal with troublesome passengers, and make quick and effective decisions. Think about some scenarios:

You are FO on a flight, the captain makes a decision you do not agree with
A passenger is angry after the flight was delayed and is shouting abuse at you
You are the captain of a flight that is low on fuel and had developed an emergency. You need to very quickly opt for continuing to the destination airport or diverting, and there are problems with either choice

Do you think you would be able to successfully deal with these types of situations in the time frame you would have to work with? Not everyone is cut out for that sort of thing, whether aspergers or neuro-typical, these are scenarios all potential commercial pilots would need to be able to deal with.
I think first you should figure out whether you like flying airplanes or not as a love of aviation and airplanes does not automatically mean you will love being at the controls. Why not go for your private license and find out? It's the first step in getting an ATPL anyway, and you could probably get a third class medical. You can then build on that if you want a career in aviation, or keep flying privately if you don't.

Very good, very complete answer. See if you can get a hold of an examiner to get his opinion before you start any major educations in that filed but don't let that hinder you to get your private license.

This is obviously a bit overdue but I strongly disagree with your answer if it's supposed to address OP's concerns about whether his Asperger syndrome would prevent him from landing a flying job with an airline. An ATPL, experience and a medical class 1 certificate are the only requirements to apply. Whether he gets a class 1 is a matter for his DME/DAME alone. The concerns that you mentions are broad-brush generalities that apply to anyone in that field. The only part for which I give you credit is that the journey from ab-initio to ATPL is a long one that begins with the first flying lesson.

@GhD because even the private license will be retired if you are asperger. At least according to the EASA regulations.

It's going to depend on the specifics and severity of your condition. You can't generalize autism spectrum disorders. But Aspergers should not exclude you from flying. Flying commercial is another story. There's only one way to find out, so if you are really serious, you should contact the certification board and find out what the challenges are going to be.
What could be more problematic is if you also have sensory integration or sensory processing issues, which often accompany an autism diagnosis. As an example, I have a son with Aspergers who also has sensory integration issues. He has a very high threshold for pain, and there is almost nothing you can do that will make him dizzy. Those are attributes that could really be useful for a test pilot or acrobatic flyer. But he is also sensitive to loud noise, which is probably not a good attribute to have in aviation.
It will probably never be proven, but there are people who believe that Neil Armstrong had Aspergers, and he was a fine pilot, as we all know. Having read plenty about Armstrong in books by Chuck Yeager and other, and from my own personal experience with Aspergers, I tend to agree.

Note though, that Neil Armstrong was not an airline pilot. He was a navy pilot and a test pilot.

... and he started his flying career at a time where there was no check for asperger.

...nor was he officially diagnosed with Asperger's or Autism

...and his ability to concentrate in an emergency and maintain engineering knowledge (Gemini 8, the final descent of the Eagle) is more appropriate for a test pilot than an airline pilot, who has to deal with a broader range of less intense situations.

Since that other answers are perhaps not overwhelmingly optimistic, I thought I'd suggest another solution that might work out.
Seeing as to that you are also interested in programming, I would look into another aviation area: Unmanned Aerial Vehicles, i.e. Drones.

No human passengers, so considerably fewer liability concerns. Proper ones are normally designed to be safe by design, i.e. terrain avoidance and flight envelope protection.
Intensive and exciting development work being done. Can generally not be said about piloting.
You can buy or build one yourself and then engineer and fly it. It's considerably more accessible.
It is a considerably less regulated industry.

One thing you should talk to your AME about is the potential for co-morbid conditions to affect your medical certification -- I have a similar diagnosis, but with co-morbid ADHD as well, and this means that best I can tell, I am ineligible for even a third class medical due to the ADHD.
So, definitely speak with an AME early on!

ADHD prevents you from getting a 3rd class? That seems surprising judging from some of the people I've heard on the radio. - haha

@reirab -- AIUI, all ADHD medications are on the "Do Not Issue - Do Not Fly" list -- and in order to function safely at well, just about anything, the medication is needed.  You might be able to get a SI medical, as per this link but part of it is a urine test....

Ah, right. I forgot about the medications.

I believe it is very unfortunate that Asperger syndrome has been included on the autism spectrum even if labeled "High Functioning…. "
I have personally worked with numerous Aspergers clients. They are capable of doing anything anyone else can do. Their weakness in understanding nuanced speech patterns, and weakness in understanding people's true intent, Etc can easily be overcome by spending time with a professional in a certain area who can teach them the typical words and phrases that are used in that field and what they really mean.
When people with Asperger syndrome do inappropriate things or say inappropriate things, they are not trying to be inappropriate. They will listen with very wide open ears to people who will actually teach them what the appropriate expectations are in different situations. I also happen to be a pilot, and my son is an airline captain. I have no doubt in my mind. A person with Asperger syndrome can become an excellent pilot. Before you go for your FAA physical, sit down with someone who can help you practice for the physical. Practicing means hearing the doctor's questions, following through with the tasks he requests, and not saying inappropriate things. There is absolutely no reason to tell the FAA doctor anything about your Asperger diagnosis.
Just like if you have a problem, where you got only A's in Calculus, but have a mental block against differential equations. You may think that that is a math disability, but it is irrelevant for most jobs. Therefore it would be foolish to write on your resume, or tell an interviewer anything about your math disability, especially when the job does not require differential equations.
"Disclosing" your "math disability" will make the interviewer think you can't do basic math. He will not understand that you completed at least 3 semesters of Calculus in university, and only tripped on a higher-level calculus!
The problem with their throwing out Asperger's as a separate diagnosis and putting everyone into the "Autism Spectrum" is that Aspys are not autistic in the sense that most understand the word.
It is a very limited syndrome. Basically Aspys understand perfectly well everything said that is clearly expressed.  They only miss situations where they need to "hear" the emphasis the speaker places on a word or phrase to understand the speaker's intent.
That is much less common in flying, since most of our communications are with short words or phrases that you will be clearly taught in flight school.
This is done so the foreign airline pilot whose "American English" is likely not their first language, can understand without confusion.
Sadly, the new inclusion of Aspys onto the Autism Spectrum causes many well-meaning people to assume people with Asperger's have some of the other autism weaknesses. Even many Aspys have read up on "the spectrum" and assume incorrectly that they have some of those characteristics.
So, absolutely first get your Class 3 medical, and get, in this order:
Private Pilot
Instrument Rating
Get some good hours, maybe 200, really master the special language of Aviation, then make up your mind.
Yes?
Get your CFI maybe, so you can earn some money instructing, while building hours instead of paying for every damn hour
Go get your Class 1 medical.
Then, GO FOR IT
Commercial
ATR

"There is absolutely no reason to tell the FAA doctor anything about your Asperger diagnosis."  You are recommending that one should commit a felony crime when you say that. Once one has been diagnosed, failing to disclose that history on the medical form is a criminal act. This answer is dangerously wrong in this regard.

Unlike organic illnesses like diabetes or hypertension, that condition is a light form of autism that can't be diagnosed objectively, and depends only upon the opinion of the examining doctor and on the information given by the person being examined. The same is true of 'heavier' mental conditions such as schizophrenia. Of course a person 'diagnosed' with 'Asperger's disease' can easily pass a first-class medical in Europe, specially if he doesn't mention that to the doctor...

I have Asperger's and ADHD but I am on medication. When I am not on medication, I am perfectly fine (just eat more then an average person). I've always wanted to fly a plane and be a pilot since I was 3 years old. I am 15 and still dreaming!.
I've been to Blackbushe airport to fly a Cessna 152 and passed. As long as you have medication, a medical certificate and can control it, I say you will be able to fly a commercial plane.

Hi Josh. Thanks for contributing, but we are looking for complete authoritative answers rather than individual anecdotes. Please do make more contributions.


text:
Is deicing fluid harmful to the environment?
How harmful is the fluid applied on aircraft to the environment? Is there any way to collect this waste fluid to minimize this, if in fact it is harmful?

The main component of deicing fluid is either Ethylene Glycol (EG, toxic) or Propylene Glycol (PG, non-toxic) (source) and depending on the category applied different amounts are used annually.
There have been studies of the environmental impact of deicing fluid, which basically states:

In water, EG is not persistent and biodegrades aerobically and anerobically.
In air, EG is not readily volatile and its atmospheric half-life is approximately 1 day
In soil EG is also not persistent and biodegrades anerobically in about 1 day
EG is disposed of and treated at standard wastewater plants

(I think the above comments also apply to PG, but somebody will have to confirm that since I can't find anything that mentions it).
PG is non-toxic and is used in quite a few products that you use every day, from pharmaceuticals to food additives and moisturizers. I can't confirm but one of the linked articles says that most of the DI fluid used in the US is PG based, which I would believe, but can't source.
And from the article quoting an EPA Report 821-R-00-0016, January 2000, Revised August 2000,

Although EPA does not use such a system, the
  U.S. Fish and Wildlife Service Classification
  System for Acute Exposures defines ‘relatively
  harmless’ as any chemical with an LC50 above
  1,000 mg/L. The test results … indicate that
  ethylene glycol and propylene glycol may be
  classified as ‘relatively harmless,’as defined by
  the U.S. Fish and Wildlife Service.

There is also one manufacturer using 1,3-propanediol which is a by-product of corn fermentation and should be relatively minor as far as environmental impact.
There is also considerable movement in airports to "go green" and recover used deicing fluid, especially considering that a larger aircraft can take more than 1000 gallons of diluted deicing solution at the rate of up to $12/gallon, quite a bit of which runs off the aircraft and onto the ground. In fact, the EPA has mandated that new airports in cold climates recover 60% of DI fluid.

Edit
It may be important to note that the point of DI fluid is to keep the snow/ice off the aircraft until it leaves the ground, not assist in flight into known ice. Depending on the fluid applied, they usually only stay on until the aircraft reaches about 100kts. This means that most of the applied DI fluid is going to end up in the airports wastewater system because most will run off the aircraft on the ramp/apron, not spread around the countryside as the aircraft flies around.

When you say "most of the DI fluid is going to end up in the airports wastewater system", do you have any idea of the proportion of fluid spread around? On an international airport with tenth of take off per hours, even if few percent of the fluid is spread around, the quantity spread around may be significant.

Maybe I wasn't clear, what I meant was that most of the DI is going to end up on the airfield, with recoverable quantities in the wastewater system. The rest of it will be in the grass/non-recoverable areas on the airfield and then will break down as per the first part of my post. I have a feeling though that 90% (my guess) of what is going to run off the aircraft is going to happen on the apron and be collected in the treatment systems, but to answer your question directly, no I can't find any data about physical quantities or % that is "left at the airport".

It's perhaps also worth noting that "biodegradable" and "relatively harmless" does not actually mean completely harmless. As a notable local example, a couple of years ago a project to run a rail tunnel under Helsinki Airport ran into considerable difficulties when it turned out that deicing fluid was seeping (and had been seeping for decades) into the bedrock under the airport, where it was, indeed, biodegraded by bacteria -- into acidic compounds that could eat away concrete. Basically, construction had to be halted and the tunnel redesigned to withstand this corrosive environment.

@IlmariKaronen Very good point, thank you.

Hopefully this helps from a deicer in Michigan.
When we deice an aircraft during deice season November- March we use a Deice pad at the airport (This is the same for all major airports) On this Deice pad we spray the aircraft and any DI fluid that falls off of the aircraft goes down a drain made specially for DI Fluid. This drain runs the perimeter of the deice pad and collects all DI Fluid that is sprayed.
When the aircraft has been sprayed it tends to sit on the deice pad for an additional 3-5 minutes to allow some excess DI Fluid to run off of the plane.
After that time the plane will begin to taxi and take off. The minimal amount of DI Fluid left of the plane will sheer off during takeoff and will land and remain at the airport. (Which has a special drainage system to care for DI Fluid)
Hope this helps everyone!


text:
What's that component between the engine and wing?
It's on most commercial aircraft and large aircraft with turbofan engines... Is there a specific name for it? Does it serve any other functions apart from attaching to the wing and feeding the engine the essentials? Has there been any aviation incidents that involved something malfunctioning or breaking inside of it? Or some other interesting things about it? Just out of curiosity! Thanks! :)

It's a hard-point called an "engine pylon".

And yes, some designs use specific points designed to fail if there is excessive force, allowing the engine to separate from the aircraft without ripping the entire wing apart which would obviously be a catastrophic event. It has happened on a few occasions.
The above image is from the Wikipedia page on the American Airlines 191 accident, where, due to a faulty maintenance practice of using forklifts for removing and reattaching the engine/pylon assembly, the aft bolts were damaged. The pylon eventually failed, allowing the engine and pylon to push up and over, separating from the wing.
Other examples include China Airlines 258 and El Al 1862.

Note: in flight 191, the engine and pylon did successfully separate from the wing but damaged the flaps mechanism, causing plane to bank then crash, killing all on board.

China Airlines 258 and El Al 1862 also killed all on board.  Has there ever been an incident where the engine separated from the wing during flight but everyone survived?

@fjw United Airlines 232 managed to make it to an airport to land, but crashed right before touchdown.

@Cole UA232 suffered complete hydraulic failure, not engine separation. (No. 2 exploded, severing all three hydraulic systems)

Am I the only person who looked at that image and immediately thought "Starship Enterprise"?

@fjw it doesn't sound to successful if it killed everyone on board.

@Keegan the engine separation was successful in the sense that the aircraft kept flying. Unfortunately due other damage it was unable to remain controllable at low speeds iirc.

It's a pylon and indeed just hold up the engine and connects it to the craft. They are designed so that excessive force will cleanly separate the engine without damaging the wing.
American airlines flight 191 had the pylon fail in midair due to mishandling of the engine during maintenance.
2 engines separated in El Al flight 1862; in this case the inboard engine separated cleanly but then slammed into the outboard engine where it did damage the wing. The same thing happened a year earlier in China Airlines flight 358.

This part is called the "pylon" or "strut" for the engine. It holds the engine on the wing, provides a path for all of the engine systems to connect, and includes the aerodynamic fairing to cover it all. The strut is designed to prevent a fire in the engine area from spreading to the wing. Mounting the engine below and forward of the wing leading edge provides some advantages over other options.
Once the strut is installed on the wing, it is intended to be permanently attached there. As shown in falstro's picture, the engine mounts are installed on the engine, and allow engines to be installed and removed as needed. When no engines are installed, a weight is suspended from the strut to balance the aircraft and prevent the plane from tipping backwards.
There are differences in design between manufacturers. Boeing struts are designed to break away from the wing under extreme loads. The strut attaches to the wing using fuse pins, which will fail at a specific loading, lower than the strength of the wing. This prevents the wing from breaking under the load, which could cause the fuel tanks to break open and start a fire. Examples of engines breaking away as designed are the Asiana 214 and Lion Air 904 incidents last year.
Airbus struts are designed to remain attached to the wing. This actually allows the structure to be less complex, and Airbus struts tend to be noticeably more narrow than comparable Boeing struts. Other methods are used to maintain safety in a crash, such as keeping the area directly above the engine as a "dry bay", which is not used to store fuel.
Here is an Airbus patent for a strut design using composite panels, which describes the strut.
As mentioned by falstro, there are multiple incidents where the structure in the pylon has failed, resulting in the engine coming off of the plane in flight. There have been both design and maintenance causes for such incidents, and both design and maintenance changes have been made to address those issues.


text:
Can foreigner fly model aircraft (quadcopter) in US without being part of an organization (like AMA)?
The title says pretty much all. I'm visiting Guam very soon and I just found out the FAA is enforcing some rules that are mostly common sense. However, one rule states "the aircraft is operated in accordance with a community-based set of safety guidelines and within the programming of a nationwide community-based organization;"
I have read the rules of AMA, but if i'm not registered with them, does this mean I can't fly my quadcopter in US territory? (non-commercial flight)
Thanks!
Lu

This answer reflects the referenced rules but does not necessarily include all laws that may apply in this situation.
The wording on the picture included in this answer is confusing. If you go to the wording of the bill, it says that the FAA:

may not promulgate any rule or regulation regarding a model aircraft, or an aircraft being developed as a model aircraft, if--
...
(2) the aircraft is operated in accordance with a community-
      based set of safety guidelines and within the programming of a
      nationwide community-based organization;

So this bill does not prohibit you from doing anything, it just says that the FAA can't make a rule specifically about model aircraft that applies to you as long as you are operating according to those rules. You still must follow any other general rules about aircraft. See the interpretation of the rule, as linked from the answer on that question, which says:

Thus, based on the language of the statute, we conclude that aircraft that meet the statutory definition and operational requirements, as described above, would be exempt from future FAA rulemaking action specifically regarding model aircraft.
...
Thus, the rulemaking prohibition would not apply in the case of general rules that the FAA may issue or modify that apply to all aircraft, such as rules addressing the use of airspace (e.g., the 2008 rule governing VFR operations in the Washington, DC area) for safety or security reasons.
...
The FAA permits aircraft operations below 500 feet when flown over open water and in sparsely populated areas. 14 CFR 91.119(c). Such operations may not be conducted “closer than 500 feet to any person, vessel, vehicle, or structure.”

It looks like there are some such "sparsely populated areas" on Guam, which should meet those requirements. Staying at least 5 miles away from the airports would also be a good idea. You can see that the southern end of the island will be your best bet:

Keep in mind that there are also additional military sites there, including one in the south, that may be sensitive to such things.


text:
What is this Lufthansa passenger jet plane, based on these three photos?
I took a plane in February 2006 from Lufthansa, I think it was an Airbus A340 but not so sure. Can someone help me identify exactly this plane? (Don't mind the ostrich)

Here is the outside of the supposed plane (not 100% sure this was the one):

Here is the inside of the plane:

And the wing :-)

So the date is February 27, 2006? Which airport was it? Which gate? Perhaps you can trace it through historical airport data?

I think the date was not properly set on the camera, I think it was more like Februrary 1st. Are those datas accessible for free online ?

If the original picture has a higher resolution you can simply read the model on the side of the fuselage just under the last "a" of Lufthansa

Now that you posted the picture of the wing this game isn't funny anymore

@pbonnefoi I just thought I would mention, it's totally OK to upload HUGE images on these SO sites.  There's never a need to make the image smaller. The web site takes care of everything.

Oops, my title edit left out a word.  Should have been "What is this Lufthansa passenger jet plane"...  Can someone with 2k rep fix that grammar instead of me submitting another suggested edit?

TLDR: The picture shows an Airbus A340-300, either registration D-AIGH or D-AIGI, parked at gate B49 at Frankfurt airport.

From the general shape of the nose of the aircraft, and the fact that the airline is Lufthansa, it is clear that we are looking at either an Airbus A330 or an A340. It is parked at gate B49 (now renamed to B42) at Frankfurt airport.
In 2006, Lufthansa was operating 10 Airbus A330-300's, 20 A340-300's and 11 A340-600's . All the A330-200 and A340-200's were phased out before 2006.
From the window arrangement & count, we can see it can't be an A340-600; too few windows between door 1R and door 2R, and too many behind 2R and the first window gap.
In your first picture, despite the low resolution, it can be seen that the first two windows behind door 1R (first door on the right hand side of the aircraft) are plugged. It also seems that behind door 2R, two windows are plugged, and then six are transparent.
In 2006, all Lufthansa A330-300 had their first and third window on the right side plugged (this can be verified by looking at pictures from 2006/2007 of each Lufthansa A330-300 aircraft registered D-AIK[A-J] on plane photography websites. (Note that the A330's of Lufthansa were reconfigured at some point, and now they fly with the first two windows behind door 1R plugged. However in 2006 this was not yet the case.)  Also the second window after door 2R was plugged. See picture below for example. This is not consistent with the observations in your picture, and hence I conclude we are looking at an A340-300.

Source: Airliners.net, photo copyright Florian Kondziela

But which A340-300...
Looking at some of the Lufthansa A340-300 fleet of the time, most aircraft had their first three windows on right side plugged, and not only the first two as in your picture. Nevertheless, if found six (registrations D-AIG[BCDFHI]) match  the window arrangement of the aircraft in your picture.
The name, written below the aircraft type, on D-AIGB (Recklinghausen), D-AIGD (Remscheid) and D-AIDF (Göttingen) is too long to match your picture.  D-AIGC was flying the Star alliance livery.
Thus remain registrations D-AIGH (Koblenz) or D-AIGI (Worms). I think your picture shows the latter.
Seen on the picture below is D-AIGI.

Source: Airliners.net, photo copyright Paul Robbins
I am confident your picture shows an A340-300.

The photo of the wing, added after this answer was created, shows an engine in the outbord position, confirming that the aircraft is indeed a four-engined A340 aircraft and not the two-engined A330. Another indicator is the fuel dump pipe sticking out of the pylon, which I think is standard on the A340, but optional on the A330 and not installed on Lufthansa's A330-300 fleet.

"Elementary my dear Watson"

How on earth did you guess the gate and airport from the picture?

@nuggethead that is a game I play often with friends. They send a picture of an aircraft they are about to board, I tell them where they go. Here we go: Two LH wide bodies, likely in Germany. Prime candidates Frankfurt & Munich. Munich has only parallel parking. Frankfurt has non-parallel / non-perpendicular parking positions. Open Google Maps 3D. Look for candidate parking positions based on the angle between the two parked aircraft. ~5 candidate positions. Look at the facade of terminal building in the background with the 5 protrusions. Is that recognisable in the 3D model on Maps? Bingo!

Now determine the exact position  of the aircraft and of the photographer by looking at details in the photo, drawing some lines on the satellite view. Positions established? Then go look for the gate map of the airport. There's the gate number. Next steps involve aircraft tracking websites and the airport information website,  but that doesn't apply here.

Absolutely amazing!

Wow I'm amazed by your sense of inquiry ! I added a photo of the wing during flight. This is my quest to know every plane I took in my life. Thank you for all the details, I love it.

Neat! How do you know the windows are plugged, and not simply that the shades are down?

@DeltaLima still, you left us with a feeling of something missing. You didn't utilize the ostrich in the investigation in any way... :-))

No seat number? No timestamp? No lat/lon for the in-flight photo? What are we paying you for anyway?! ;) Only joking. Great sleuthing.

@TypeIA, give me break, that in-flight photo was only added this morning, and had to do work that actually pays in between! Approximate coordinates of the in flight picture: 54.381380, -56.84272 taken in a northwesterly direction. Destination Toronto?? I could give an approximate time based to shadow on the wing, and typical schedules for westerly transatlantic crossing, but I leave that up to the audience!

@TypeIA seat 46D BTW, but that is superfluous given the seatmap in the other answer. :-)

@Kenn Sebasta the difference between a plug and shades down windows is clearly visible. In case of the shades, there is a windows (transparent & thick) and an off-color shade. In case of a plug, there is a panel flush with the fuselage in the same paint. The only tell-tale signs that it is a plug and not just fueslage is the small rubber seal around the edge. Have a look at the first picture (the A330) in my answer, just aft of the second door (2R). The first window is blinded with a shade, the second has a plug, the third is open.

If you look at the fleet history, it needs to be at least 17 years old (as of 2023), which narrows it down to an:

Airbus A319-100
Airbus A340 (3 subtypes)

The A340 is very long, so judging by the photo, I think it's an Airbus A319-100.
As for as the fluffy thing, I believe that is a Chocobo.

Pretty clear the outside and inside pictures aren't the same aircraft.  The interior is a wide body, looks like seven seats with the dual aisle.

The number of doors in the OP's picture are 4, but the A319-100 seems to only have 3. The A340 has 4, so would be more likely of the two.

Downvoted. The shape of the flight deck windows very clearly identifies this as either an A330 or A340. Lufthansa has operated both A330 and A340 aircraft during 2006 and many years before and after.

What is listed is average age, not oldest age, so the age doesn't narrow it down at all. Also that looks nothing like a chocobo.

Thanks for trying :-) Down votes are a bit hard.


text:
Would an accurate weight of a loaded aircraft be helpful?
If a commercial aircraft's actual weight at takeoff is accurately known (instead of being estimated), can this help with use of thrust, optimal altitude, etc and therefore fuel savings, emissions etc.?

Welcome to aviation.SE! I suggest you review some of the existing questions we have here (e.g. this one); aircraft weight is usually already known quite accurately at takeoff.

Also this one

Of course, the common practice of using average weights for passengers isn't always reliable. See "The Bod Squad" on this page.

Or https://en.wikipedia.org/wiki/Air_Midwest_Flight_5481

Indeed, knowing the actual weight of the aircraft could have saved lives.

A friend of mine was FO on a regional jet with 50 passengers. During the take-off, the PIC could not rotate the plane at the calculated VR, but only much later. They reported the incident during the flight. The luggage containers were re-weighted at the destination, and it turned out that one of the containers had a grossly wrong weight recorded at the origin.
Weighing mistakes can end in a disaster, especially for smaller jets. Systematic weighing of ready to launch planes would eliminate this risk. I am not aware of an accident caused by this kind of weighing mistake, but surely there have been accidents due to overloading or wrong load distribution.
The technology to build load sensors into the undercarriage is available and it appears that a few planes are equipped with it.
On the other hand side there must always be a risk assessment with a trade-off between costs, likelihood and severity.

And indeed it has caused crashes. Incorrect weight calculations on takeoff can be bad enough, but as in your friend's case are usually corrected for quickly enough. On approach however they can lead to incorrect approach and flap speeds, causing low altitude stalls.


text:
What were the U.S. Air Force's first 2-crew fighter planes?
The Navy has had 2-crew planes since at least as early as 1944 with the Grumman F7F Tigercat but when did the U.S. Air Force adopt 2-seaters. Does the Navy prefer 2 crew and the Air Force prefers 1? Was the McDonnell F-101 Voodoo one of the first AF 2-crew?

Are you asking specifically about fighter aircraft? Because at the time the US Air Force was formed (18 SEPT 1947), they basically just took everything that the US Army Air Corps had and flew that. One of the first operations for the US Air Force was Operation Vittles and used C-54 Skymasters which had a crew of 4.

@RonBeyer not sure but the question seems to be focusing on fighters.

Does the Navy prefer 2 crew and the Air Force prefers 1?  You need to break that out as a separate question rather than asking that within the body of a different question.  Even so, it's basis is doubtful.  In the 1960's the Navy was flying both F-4 (two seats) and F-8 (one seat) at the same time; fast forward twenty years (80's)  and the Navy is flying 2 seat (F-14) and one seat (F-18) at the same time.  Again, that sub question belong as its own question.  Feel free to ask it as another question.  SE sites are designed for "one question / one answer" as the normal mode.

The US Army Air Corps has flown bombers with 4+ crew members since the 1920s, for example the Huff-Daland LB-1 introduced in 1927.
In the WWI and interwar era, a few biplane fighters carried an observer/gunner; the Berliner-Joyce P-16 introduced to the USAAC in 1932 was one such. As aircraft speeds increased through the 1930s, the open-cockpit flexible gun mount became less practical and the weight penalty of a second crew member in an enclosed turret was rejected for fighters.
During WWII the introduction of radars small enough to put on a plane led to the development of "night fighters" or all-weather fighters with a second crew member dedicated to operating the radar equipment. (This Q&A discusses the tradeoffs between single-crew and multicrew designs in more modern combat aircraft.)
The long-range P-82/F-82 Twin Mustang entered USAF service in early 1946. Early models had two identical crew cockpits allowing pilots to alternate control on long flights; later night fighter versions introduced between 1946 and 1948 put the radar operator in the right cockpit.

Depending on what you consider a fighter, the Northrop P-61 Black Widow night fighter entered service with the USAAF in 1944 with a crew of 2 or 3 (pilot, radar operator, and optional gunner).

The Black Widow wasn't a traditional dogfighter, but carried radar and heavy guns to intercept bombers at night.
Similarly, the P-70 was a night fighter in USAAF service from 1942, but it was a conversion of a light bomber design.

The first two-crew fighter aircraft to enter service with the US Air Force was the Lockheed F-94 Starfire.

Source: Wikipedia Public Domain
The aircraft's first flight was on April 16, 1949 and entered service in May of 1950.

Thanks Ron Beyer. Do you know about the AF pattern with 2 seater fighters? Was the F-101 Voodoo revolutionary at all in it being a 2 seater for the U.S. Air Force?

It may help to answer the original question to explain why two crew were needed here and if that trend continued in later aircraft.

I would have to agree that the P61 Black Widow, which carried the formal designation of Pursuit (fighter), was the first multi-crew FIGHTER in the US inventory. It was a dedicated night fighter, and like most multi-crew intercepters, carried additional crew to work the complex weapons systems (or radar, in the case of the P61).
Interesting note: due to special wing flaps, the P61, while not much smaller than a B-25, could roll at about the same rate as a Mustang, though obviously it would lose a lot of airspeed from sharp turns, and take longer to get that speed back.
During the war, a 2 seat night fighter variant of the P38 Lightning, the P38M was produced in small numbers (75 total).
The British did field the Bristol Fighter in WW1, and it was quite successful. They tried this again in WW2 with the Boulton Paul Defiant that was a dismal failure. Plus the German BF 110, which wasn't as bad, but not really competitive with single seaters.

I didn't think about WWI and interwar era fighters; USAAC had a 2-seat biplane fighter in '32.

Looks like the US built copies of the Bristol during WWI as well.


text:
Can an instructor sign off for my check ride if I didn't fly with him since a year?
I am at the end of my training as a student pilot with an overkill amount of flying hours, but I had a couple of complications in the way.

I flew with my old instructor (instructor A) for about 3 years, and he signed me off for everything but the check ride.
When it was time for me to go to college, I had to find a new instructor (instructor B) and we trained for about a year until he decided it was about time I go for the check ride. Sadly our plane had engine issues and I had to cancel my check ride.
So I had to go back home to my old instructor (instructor A) who I haven't flown with for about a year. The last time we flew, he also said I was ready for the check ride, but that was about one year ago.

My question is this: Can my hometown instructor (instructor A) sign my off for my check ride even though I haven't flown with him in a year?
I stayed current with my flying and I even flew the same type of plane (One was a Cessna 172n and the other was a Cessna 172m).

You are putting instructor A in a delicate situation because he was not flying with you. Better go to instructor B and ask him do sign off. Maybe he can send you a letter o mail to you the pappers.

How long ago was the check ride you cancelled? Didn't instructor B endorse it then?

No.  Instructor A needs to provide at least three hours of training in preparation of the practical test within two calendar months of the checkride.

§61.39   Prerequisites for practical tests.
(6) Have an endorsement, if required by this part, in the applicant's logbook or training record that has been signed by an authorized instructor who certifies that the applicant—

(i) Has received and logged training time within 2 calendar months preceding the month of application in preparation for the practical test;
(ii) Is prepared for the required practical test; and
(iii) Has demonstrated satisfactory knowledge of the subject areas in which the applicant was deficient on the airman knowledge test;

§61.109   Aeronautical experience.
(a)  For an airplane single-engine rating...

(4) 3 hours of flight training with an authorized instructor in a single-engine airplane in preparation for the practical test, which must have been performed within the preceding 2 calendar months from the month of the test

§61.103   Eligibility requirements: General.

(f) Receive flight training and a logbook endorsement from an authorized instructor who:
(1) Conducted the training in the areas of operation listed in §61.107(b) of this part that apply to the aircraft rating sought; and
(2) Certified that the person is prepared for the required practical test.

Instructor A has to provide the required training to the applicant before signing him off for the practical test.  I would agree it doesn't have to be within two calendar months... but three hours are required from an authorized instructor with two calendar months.  However, I would not, under any circumstance, sign off an applicant without at least three hours of training within the preceeding two calendar months.  How else would I know they are prepared for the practical test?

I'm not sure it reads like that... Instructor A should be able to sign off for the check ride as long as they can verify that any instructor has provided and logged training time within the previous 2 calendar months. All Instructor A has to do is verify that the student received instruction, it doesn't necessarily need to be by the same instructor.

@RonBeyer.  I read 61.103 as a requirement for training before I give out my endorsement for a practical test.

Any instructor can sign you off as ready, with a couple of caveats.
First, the instructor is certifying that you're ready for the test. The only way to know that for sure is to fly with you until he's satisfied that you really are ready. In theory he could pencil whip your application, but if you fail the checkride spectacularly the DPE and even the FAA would probably have some questions for him. And too many failed candidates would make his CFI renewal process more difficult.
Second, in order to take the private pilot checkride you need several logbook endorsements (see AC 61-65 for all the details) plus an IACRA recommendation. One of those endorsements is required by 61.103(f), which says the endorsing instructor must have instructed you himself:

(f) Receive flight training and a logbook endorsement from an
  authorized instructor who:
(1) Conducted the training in the areas of operation listed in
  §61.107(b) of this part that apply to the aircraft rating sought

The IACRA process also requires the recommending instructor to confirm that he did instruct you personally (see the IACRA instructions 11.2.4):

By electronically signing this document I certify that:
I have personally instructed the Applicant and consider this person
  ready to take the test.

So in summary, instructor A can certainly endorse your logbook and recommend you in IACRA, but he has to certify that he's instructed you and you're ready for the test. That means you have to expect to fly with him first.
Alternatively, go back to instructor B and get him to do it. But it isn't clear from your question how long it's been since you flew with him (or any instructor) and he might also want to fly with you again first.


text:
Why would an airplane's nosewheel bounce during landing?
A pilot recently had an issue involving the nose wheel bouncing several times before settling down during landing.  Setup was as follows:

Cessna 162 Skycatcher
Simulated short field landing.
Full Flaps, per POH
Approach speed 50 KIAS per POH
Headwind 6 knots
Good condition, paved runway
Pilot has 30 hour in this specific airplane, ~100 landings in this specific airplane and has not experienced this before.

During the touchdown, the following happened:

Pilot flared at correct altitude.
Plane touched down, main gear first.  Main gear remained on runway.
Nose wheel then bounced 3-5 times before settling down on the runway.

Note: Bounce was not pronouced enough to cause a tail strike
This felt to the pilot like a PIO, but it was not a Porpoise as described in this post.
Questions:

Is this a PIO?
Why did the nosewheel bounce?
How can the pilot prevent this from happening in the future?
Should this occur again, how can the pilot minimizes the nose bounces?

Did the pilot hold the yoke back and allow the nose wheel to settle by itself, or did the pilot relax the yoke?

I don't think this can be usefully answered here.  Fly with an experienced pilot or instructor and get feedback from them on a specific flight.

In theory this could be due to an improperly serviced Oleo strut, say too much air and insufficient hydraulic fluid. But without inspecting the strut I can't say.

Sounds most like the pilot released back pressure  on the control stick abruptly once the main wheels touchdown. The idea here is that you gently lower the nose wheel to the pavement once the mains are on the ground in order to prevent that kind of a bounce.   As I recall the Cessna 162 has a tendency to bounce on the nose wheel as well as to porpoise if the landing attitude is not done correctly it's just a quirk of that airplane.


text:
What is the relation between pressure and airflow speed above an airfoil?
Does decreased pressure on the top surface of an aerofoil cause high velocity airflow or does the high speed airflow result in decreased pressure?

Related on [physics.se]: What really allows airplanes to fly?, and linked questions.

Both pressure and velocity are related: The total energy of an air molecule outside of the boundary layer is constant and the sum of its pressure and its velocity component. Mathematically, the energy per unit of volume is
$$\frac{\rho}{2}\cdot v^2 + p = const$$
which is actually the simplest form of Bernoulli's equation which neglects changes in altitude and temperature.
In the end, it's not this causes that, but both components fluctuate in sync and combine to a constant total.
Nomenclature:
$\rho\:\:$ density
$v\:\:$ speed
$p\:\:$ pressure

Reducing the cross-section area
When air encounters the airfoil, the streamlines over the top surface are compressed, because the surface is an obstacle pushing them vertically upwards, and the rest of the atmosphere prevents them from moving freely in block upwards. Note this reduction of area is widely accepted as real, but is not well explained.

This would work the same way for the other side of the cylinder, as atmosphere pressure exerts in any direction, normal to the surface.
Increasing speed
If we assume a simplified case of little change in density (nearly incompressible fluid), the same quantity of air must go through a smaller area in the same time, and to do that it "must" accelerate. This is similar to what happens to water in a garden hose: When squeezing the extremity water accelerates at this location relative to the rest of the hose.
Decreasing pressure
If we still assume a nearly incompressible fluid, and neglect the effect of viscosity then, per Euler's equation, an infinitesimal variation of velocity $dV$ leads to a variation of pressure $dP$ equal to $-\rho VdV$ ($\rho$ the air density, $V$ the velocity).
We see pressure varies inversely to the velocity. Therefore a cross-section area reduction leads to a velocity increase, which in turn leads to a pressure decrease.

If you need to put a name on this effect, then this is Bernoulli's principle! More on Euler and Bernoulli equations: Fluid Mechanics, Euler And Bernoulli Equations
Which one change first, pressure or speed?
Pressure and velocity in a fluid carry some energy (pressure energy, which is a kind of potential energy, and kinetic energy). The total energy is constant.
The obstacle changes the ratio between potential energy (pressure) and kinetic energy (speed). None change first. It's like action and reaction, their existence is linked and simultaneous.

To compare: With a full cylinder, pressure will be the same top and bottom. With a usual airfoil with a water droplet section, the principle will not change. When adding the AoA (which is not possible with the cylinder indeed), the pressure will be different on each side, and the accelerated airflow will be deviated down, creating aerodynamic lift. Using  the steady flow assumptions (incompressible, inviscid and irrotational) is no more possible (e.g. I believe the flow on bottom side will be significantly subject to viscosity, air will be slowed down, and pressure will increase).

The cross-sectional area is not (necessarily) reduced!. Remeber, that a thin, flat plate, at slight angle to the air stream, produces lift, and does so using the same mechanism. So while what you say is true, it does not describe what happens around the wing well.

@JanHudec: The question is not about lift, only pressure/velocity relationship. With all due respect for your expertise, I believe the flat plate also reduces the cross section of the airflow at appropriate Reynolds numbers and AoA,

@mins, well, after all the Bernoulli's equation still does hold, so the faster flow must be using less space. There is, however, no obvious argument why it should be the case, so it is not usable as explanation (speaking of cause in physics not always makes sense and this is such case).


text:
Relation between drag and aspect ratio
How does increasing the aspect ratio decrease the drag over the wings? Wouldn't the various types of drag affect over the wings in proportion to the increasing aspect ratio?

Related: http://aviation.stackexchange.com/questions/5047/how-does-chord-length-affect-wing-design/5056?s=1|0.2328#5056 and especially http://aviation.stackexchange.com/questions/716/what-dictates-the-aspect-ratio-of-an-aircrafts-wing/8797#8797

I think the later is related so much that it can be considered duplicate.